Fuel composition for diesel engines



1 3,002,827 FUEL COMPOSITION FOR DESEL ENGINES Merrell R. Fenske, State College, Pa., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Nov. 29, 1957, Ser. No. 609,443

6 Claims. (Cl. 44-57) The present invention concerns improved fuel compositions for use in high speed compression-ignition engines, or diesel engines. More particularly, the invention relates to novel fuel compositions of a type not heretofore employed in such engines, thereby augmenting the supply of diesel engine fuel.

In recent years the use of diesel engines has steadily increased and there is every reason to believe that the total horsepower output furnished by diesel engines will continue to increase rapidly. In the 14-year interval from 1941 to 1954, the demand for diesel fuel increased six-fold, as compared to slightly less than a two-fold increase in the demand for petroleum products as a whole. To meet the potentially increased demand for diesel fuels, it is desirable to find new sources for such fuels as well as improve their quality.

It is one object of the present invention to utilize hydrocarbon or petroleum fractions not heretofore incorporated into high-speed diesel fuels and at the same time to produce a fuel with a minimum viscosity of about 1.2 centistokes at 100 F., with a low freezing or separation point, and with a high specific gravity so the heat of combustion per unit of volume will be high, thus attaining good mileage, or a low specific fuel consumption. A further object is to provide a fuel with increased volatility and good cold starting properties, free from knock or ping, and with low smoke and exhaust nuisance properties. The viscosity of the fuel is important in keeping down fuel pump wear and in expediting the accurate metering of the fuel by the injection pump.

In accordance with the present invention, entirely acceptable diesel fuel compositions are prepared by blending volatile gasoline hydrocarbons of low octane number with highly nucleated, or polynuclear, aromatic hydrocarbons and with non-benzenoid, hydrocarbon-soluble, hydroxylated hydrocarbons, or alcohols, the latter having at least 6 carbon atoms and boiling below about 750 F.

More specifically this fuel for high speed compression ignition engines is made up of a mixture of from about 30 to 55 weight percent of low octane volatile petroleum gasoline hydrocarbons boiling in the range of about 150 to about 450 F., from about 25 to about 40 weight percent of nucleated aromatic hydrocarbons having from about 2 to 4 aromatic rings per molecule and boiling in the range of about 450 to about 750 F., and from about 15 to about 30 weight percent of a non-benzenoid, hydrocarbon-soluble, alcohol having at least 6 carbon atoms and boiling below about 750 F. The volatile petroleum hydrocarbon components of low octane number usually have an octane number of 50 or lower.

The above mentioned fuel composition will have a viscosity of at least 1.2 centistokes at 100 F. and preferably from about 1.4 to 3 or more centistokes at 100 F to avoid the danger of excessive fuel pumpwear. The composition is also a good lubricant for the fuel pump. This fuel has a low separation point, or cloud or pour point; usually this value is below 0 F. It is clean burning.

The volatile gasoline components of the compositions of this invention are obtained by using hydrocarbon fractions high in parafiins having a large part of their carbon skeleton in relatively long chains, i.e. about 6 carbon atoms or more. Normal heptane and normal octane are good components. Straight run naphthas boiling in the range of about 150 to 450 F. with octane numbers below 50 are also suitable. Raflinates from the liquid tet , centistokes.

extraction of thermally or catalytically cracked heavy naphthas, or raffinates from the extraction of hydroformates, are good components for this fuel. This is important, for the extracts from such operations are high quality or premium components for gasoline, or spark ignition engines while the rafiinates may be employed in the present invention.

The polynuclear aromatic hydrocarbons for the compositions of this invention may be obtained from the cycle stocks of a catalytic cracking operation, or from the solvent extraction of petroleum fractions having substantial proportions of these aromatics. These fractions may be thermally or catalytically cracked distillates, or fuel or light tube oil fractions boiling in about the 400 to 750 F. range. Thus if a fuel oil or catalytic cycle stock is extracted with a suitable selective solvent the desired highly nucleated aromatics will be obtained in the extract, and the raflinate will have improved burning properties for use as a fuel oil, or as an improved feed stock for a catalytic cracking operation. These aromatics are important components in these fuel compositions because they have a much higher viscosity than the corresponding paraflins, and they have a high heat of combustion per gallon, which provides good fuel economy. They are also good solvents.

The hydroxylated hydrocarbons, i.e. alcohols, used in this invention have one or two hydroxyl groups per molecule. The single hydroxyl compound, or simple alcohol, should have at least 6 carbon atoms and preferably 8 or more. As will be indicated, a dihydroxy compound or glycol is much more viscous than an alcohol, but it is also less soluble in hydrocarbons than the alcohol. In general, a glycol will have to have a higher molecular weight to attain the same solubility as the alcohol. For the same volatility, an alcohol is much more viscous than a hydrocarbon and usually of a higher specific gravity. An aliphatic alcohol of the same number of carbon atoms as a parafiinic hydrocarbon has about the same heat of combustion per gallon, but is substantially higher boiling and much more viscous. For the same boiling point, an aliphatic alcohol has a lower heat of combustion than a paraffin hydrocarbon, although this difference is not necessarily great. When the aliphatic alcohol has 8 or more carbon atoms its heat of combustion is within 5% or less of that of a paraifin hydrocarbon of the same boiling point. Thus, it is usually desirable to use higher boiling alcohols. Not only are their burning or anti-knock properties generally better, but there is a higher heat of combustion per gallon. This makes for economy or a lower specific fuel consumption. A few examples illustrate this point.

Cyclohexanol has a boiling point of 160 C. and a viscosity at 100 F. of 25 centistokes. A parafiin hydrocarbon of the same boiling point has about 1 centistoke viscosity at 100 F. Normal hexanol has a boiling point of 157 C. and a viscosity at 100 F. of 3.7

A glycol is still more viscous. For example, Z-ethylhexanediol-lfi has a viscosity at 100 F. of about 125 centistokes and a boiling point of 470 F. A paraffin hydrocarbon of this boiling point has about 2 centistokes viscosity at 100 F. Dipropylene glycol has a viscosity of 20 to 30 centistokes at 100 F.

The alcohol is preferably of the paraffinic or chain j type although cyclic or naphthenic alcohols are suitable. Preferably the aliphatic alcohols have a predominant number of their carbon atoms in a relatively straight chain structure. However, tridecyl alcohol, made from propylene by the 0x0 process, has been found to be satisfactory in these fuels. This 0x0 alcohol has not less than 6 to 10 of its carbon atoms in a linear chain. The blending viscosity of this tridecyl alcohol in nheptane is about 15 centistokes at F. The synthesis of x0 alcohols from olefins is now well known in the art and involves reaction of the olefins with carbon monoxide and hydrogen in the presence of a cobalt or iron catalyst in a two-stage process. In the first stage the olefinic material and proper proportions of CO and H are reacted in the presence of the catalyst to give a product consisting predominantly of aldehydes. The aldehyde material is then hydrogenated in the second stage to furnish the corresponding alcohols.

The following experimental results serve to illustrate the practice of the present invention. Various fuel blends were prepared and tested in a Mercedes-Benz automobile powered by a watercooled, 4 stroke, diesel engine having a brake horsepower rating of 40 at 3200 rpm. using a 19 to 1 compression ratio. The automobile was fitted with glass burettes so that the Various fuel compositions could be measured accurately to get fuel consumption data. Suitable valves were fitted into the fuel lines to enable the engine to be switched from one test fuel to another. Provision was made for purging the fuel lines when changing from one fuel composition to another.

The tests were made over a ten-mile stretch of road, providing a combination of flat and hilly terrain. Data obtained when traveling in both directions over the test stretch were averaged. The same motor oil was used in all of the tests. This was a heavy duty, high quality, high viscosity index oil in the SAE 20-30 viscosity range. Oil changes were made at 2000 mile intervals.

The composition, viscosity, and specific gravity data for the blends tested are given in Table I. The V.M. and P. naphtha employed in preparing some of these blends was a varnish makers and painters naphtha prepared from a Michigan virgin gasoline and had a boiling range of 155 to 325 F. and an octane number of 30 to 40. The close-cut naphtha was a straight run naphtha known commercially as 'No. 1 Varsol. It had a boiling range of 300 to 400 F. and an octane number below 50. Both these naphthas are characterized by containing predominantly parafiinic and naphthenic hydrocarbons and not more than aromatic hydrocarbons. They would be poor fuels in a gasoline engine because they would knock badly.

The polynuclear aromatic hydrocarbon fraction was a commercially available high boiling aromatic solvent, known as Sovaloid C. It had a boiling range of from about 550 to about 700 F., and consisted essentially of 100% aromatics in which 2- to 4-ring, highly condensed aromatic hydrocarbons predominated. Its viscosity at 100 F. was 16 centistokes and its specific gravity was 1.06. Its pour point was -30 F. This material was selected as typifying the aromatic hydrocarbons available in catalytic cycle stocks.

A regular No. 2 heating oil, or diesel fuel, was used as a reference standard for rating the fuels listed in Table I. This standard fuel was a conventional hydrocarbon fraction boiling within the range of about 300 and 700 F, with a specific gravity of 0.83 at 60 F., a cetane number of 50, and a viscosity of 2.5 centistokes at 100 F.

Blend A in Table I was found to be one of the most satisfactory fuels tested. It performed more smoothly and quietly than the standard reference No. 2 fuel. Low temperature starting was good and the burning was clean. No trouble whatever was experienced when blend A was tested for 500 miles, both in traffic and over the open road. It was a smooth, well performing fuel that was found to be at least as good as a commercial diesel fuel in all respects. The rate of fuel consumption for a given miles per hour speed was as good as the standard reference No. 2 fuel.

Fuel B in Table I differed from composition A in that the content of the aromatics was increased from 30 to 35 percent while reducing the normal heptane content from 25 to 20 percent. This fuel was also found to be very satisfactory.

Fuel C in Table I was satisfactory in a warm engine. There was no smoke or knock at any speed. Acceleration was good, and the mileage was as good as the reference standard No. 2 fuel. It was not as good as fuels A and B in cold starting at 40 F. There was more smoke during start up and the engine was rougher.

Fuel D in Table I performed well, even with ambient air at 40 to 50 F. There was no low speed knock, no smoke, and the acceleration was good. Fuel consumption was also as good as the reference standard No. 2 fuel.

Fuel E in Table I behaved satisfactorily. The engine was smooth and acceleration was good. Fuel consumption was about 10 percent more than the standard reference fuel. Its viscosity of 1.2 centistokes made this fuel just borderline on the viscosity requirement.

Blends F and G were similar in that each contained 40 percent of polynuclear aromatics and 20 percent of octanol-2, but the volatile component in blend F was provided by 40 percent of V.M. and P. naphtha, whereas in blend G the volatile component was provided by 40 percent normal heptane. Blend G behaved satisfactorily, producing no smoke, knock, or high speed ping. Blend F showed some tendency to ping at speeds in the range of 45 to m.p.h., but it was otherwise satisfactory.

Blend I-I contained 45 percent of polynuclear aromatics and gave no trouble in starting at F. There was no low speed knock, but an occasional ping in the 40-60 m.p.h. range. Acceleration was good. There was difliculty with cold starting at 40 F. There was considerable smoke and the engine was rough and noisy, although these characteristics disappeared when the engine warmed up. Fuel consumption was about as good as the standard reference No. 2. fuel.

Blend J was not satisfactory in that at speeds above 50 m.p.h. there was a steady ping, but otherwise the power was normal. It appears that the ignition delay was sufiiciently great so that the fuel could not burn fast enough to accommodate such engine speeds. Also, the viscosity of this blend was too low for acceptable performance.

TABLE I Weight percent of component in blend Blend Component A B O D E F G H I K n-Heptane 25 20 40 40 25 V.M. & P. Naphtha 1 20 20 25 40 40 45 15 Close Cut Naphtha 3 p 25 15 Polynuclear Aromatics 30 5 30 35 30 40 40 45 50 30 n-Decanol 25 25 20 25 10 0ctanol- 30 20 20 2-Ethylhexanediol-1,3 15 Viscosity, 05., at F 1. 5 1. 6 1.6 1.8 1.2 1.4 1.4 1. 5 1.0 1.4 Specific Gravity, 60/60 F 0.83 0.84 0.85 0.85 0.82 0.82 0.83 0.87 0.83 0.84

Straight run distillate of F.325 F. boiling range, containing about 12 volume percent n-heptane and 40 volume percent n-octazne 9 Straight run naphtha ht 300 to 400 F. boiling range.

Blend K in a warm engine performed rather well. The engine was smooth and acceleration good. However, there was some high speed ping. Starting at 50 F. was satisfactory. One percent of amylnitrate was added to this fuel and the ping at all speeds was absent. The engine was smooth. It could not be made to knock even when the engine was decelerated and then rapidly accelerated. Fuel consumption was as good as the standard reference No. 2 fuel.

The viscosity of a mixture of 50 weight percent normal heptane and 50 percent 2-ethyl hexanediol-1,3 is 3.5 centistokes at 100 F. There is some phase separation at +35 F. However, a blend containing 40 weight per cent of normal heptane, 20 weight percent of the 2-ethylhexanediol-LS, and 40 weight percent of the polynuclear aromatics was clear and fluid to below F. The viscosity of this blend is 1.7 centistokes at 100 F. This indicates the good solubilizing action of the aromatics.

The foregoing results indicate that up to about 40 percent of polynuclear aromatics can be tolerated if blended in fuels as shown. As noted above, blend H, containing 45 percent of polynuclear aromatics was not wholly satisfactory in performance and blend 1, containing 50 percent aromatics, was not acceptable. The results also indicate that the maximum amount of low octane petroleum distillate component that can be tolerable is about 55 percent, since blend K was somewhat borderline in performance.

It should be emphasized that all these fuels had a good response to the conventional diesel anti-knock agents or ignition promoters such as amylnitrate or nitrite. Whenever there was incipient knock or steady ping this could be eliminated, with correspondingly smoother engine operation and acceleration, when from 0.5 to 1 percent of .amylm'trate was added. Cold starting was also improved.

It is within the contemplation of this invention to employ other known ignition promoters, oiiiness agents, pour point depressants and corrosion and oxidation inhibitors in the blends of this invention it such use is found necessary or desirable. The preferred ignition promoters are aliphatic nitro compounds such as amylnitrate, amylnitrite, nitropentane, isopropylnitrite, nitroalcohol nitrates, and the like, employed in about 0.5 to 1.5 percent concentration.

It is also possible to blend the fuels of this invention with conventional diesel fuels, such as the standard reference fuel No. 2, without any objectional eifects, either while operating the engine, or in storage. It is evident, therefore, that a new type of diesel fuel has been found that can be used alone or in combination with conventional diesel anti-knock agents. Thus a substantial contribution has been made to the supply of diesel fuels, especially those for high speed engines, and a refiner can blend diesel fuels from stocks that were otherwise not suitable by themselves.

The above description and examples have been presented for the purpose of illustrating the invention and are not intended to limit its scope. It is intended that the appended claims include within their scope any modification or variation from the description or the examples that conforms to the spirit of the invention.

What is claimed is:

1. A fuel composition for a compression ignition high speed engine comprising a mixture of from about 30 to about weight percent of a low octane petroleum distillate produced as a rafiinate from the extraction of a naphtha, said distillate boiling Within the range of about 150 to 450 F., from about 25 to about 40 weight percent of polynuclear aromatic hydrocarbon produced as an extract from a petroleum fraction boiling within the range of about 400 to 750 F., and from about 15 to about 30 weight percent of a non-benzenoid hydrocarbon-soluble alcohol having at least 6 carbon atoms and boiling below about 750 F., said fuel having a viscosity of at *least 1.2 centistokes at F.

2. The fuel composition of claim 1 containing from about 0.5 to 1.5% of an aliphatic nitro compound selected from the class consisting of nitroalkanes, alkyl nitrates, alltyl nitrites and nitroalcohol nitrates.

3. The fuel composition of claim 1 where the alcohol has at least 6 carbon atoms in a straight chain structure, and is normally liquid.

4. The fuel composition of claim 1 where the petroleum distillate boiling in the range of about to 450 F. has an octane number below about 50.

5. A fuel composition for use in high speed diesel engines which consists of from 20 to 25 weight percent normal heptane, about 20 weight percent low octane naphtha having a boiling range of F. to 325 F., about 25 weight percent normal decanol and hem 35 to 30 weight percent of polynuclear aromatic hydrocarbons of from 2 to 4 cyclic rings, said aromatic hydrocarbons boiling in the range of 550 F. to 700 F., said fuel having a viscosity of at least 1.2 centistokes at 100 F.

6. An improved method for operating a high speed diesel engine which comprises feeding to the said engine a fuel composition comprising in major proportion a mixture of from about 30 to about 55 weight percent of low octane petroleum hydrocarbons boiling in the range of about 150 to 450 F., from about 25 to about 40 weight percent of polynuclear aromatic hydrocarbons boiling in the range of about 450 to 750 F., and from about 15 to about 30% of a non-benzenoid hydrocarbonsolubie alcohol having at least 6 carbon atoms and boiling below about 750 F., said fuel having a viscosity of at least 1.2 centistokes at 100 F.

References (Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Journal of Institute of Petroleum Technology, vol. 27,

October 1941, Means of Improving Ignition Quality of Diesel Fuels, by Nygaard et al., pages 348-368. 

1. A FUEL COMPOSITION FOR A COMPRESSION IGNITION HIGH SPEED ENGINE COMPRISING A MIXTURE OF FROM ABOUT 30 TO ABOUT 55 WEIGHT PERCENT OF A LOW OCTANE PETROLEUM DISTILLATE PRODUCED AS A RAFFINATE FROM THE EXTRACTION OF A NAPHTHA, SAID DISTILLATE BOILING WITHIN THE RANGE OF ABOUT 150* TO 450*F., FROM ABOUT 25 TO ABOUT 40 WEIGHT PERCENT OF POLYNUCLEAR AROMATIC HYDROCARBON PRODUCED AS AN EXTRACT FROM A PETROLEUM FRACTION BOILING WITHIN THE RANGE OF ABOUT 400* TO 750*F., AND FROM ABOUT 15 TO ABOUT 30 WEIGHT PERCENT OF A NON-BENZENOID HYDROCARBON-SOLUBLE ALCOHOL HAVING AT LEAST 6 CARBON ATOMS AND BOILING BELOW ABOUT 750*F., SAID FUEL HAVING A VISCOSITY OF AT LEAST 1.2 CENTISTOKES AT 100*F. 